This invention relates to a fluid pressure braking system having a pair of reservoirs, and valving mechanism which controls communication of fluid pressure to the reservoirs, protects the reservoirs in case of a leak in the system, and is capable of communicating either of the reservoirs to the spring applied, fluid pressure released parking brakes on the vehicle so that the parking brakes can always be released after a single failure of the vehicle service brake system.
To meet Federal regulations, vehicle manufacturers have heretofore used a trailer fluid pressure braking system having three reservoirs. Two service reservoirs were needed to supply the required volume for the service braking system. A third reservoir was required to provide an isolated source of fluid pressure which could be used to release the vehicle spring applied, fluid pressure released parking brakes upon a failure of the service brake system. A revised interpretation of this regulation does not require that the parking brake release pressure be supplied from an isolated source if the parking brakes can be released at least once after a single service brake system failure. Accordingly, the present invention proposes a trailer fluid pressure braking system having but two service reservoirs, but which also includes appropriate valving and interlocks to isolate the reservoirs from one another so that a single service failure will deplete, at most, only one of the reservoirs, and also includes appropriate valving to communicate either of the reservoirs to the trailer spring applied, fluid pressure released parking brakes so that the latter may be released if any one of the reservoirs has failed.